The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a magnetic data storage and retrieval system having improved magnetoresistive head resistance measurement accuracy.
In magnetic data storage and retrieval systems, a magnetoresistive (MR) head utilizes MR elements to sense the selective magnetization of tracks on a magnetic data storage medium. A typical MR element is formed from an alloy of materials so as to have an electrical resistance which varies in the presence of a magnetic field. By passing a bias current through the MR element, the selective magnetization of a corresponding track can be determined in relation to variations in voltage detected across the MR element.
The sensitivity of an MR head depends on many factors. One of the most significant factors is the bias current provided to the MR head. The ability to read a signal from a magnetic medium is, in part, a function of the amount of bias current supplied to the MR head. Signal sensitivity can be increased by increasing the amount of bias current supplied to the MR head. Therefore, increased bias current will generally produce an improved signal-to-noise ratio and will therefore result in lower error rates.
However, excessive bias current can significantly shorten the useful life span of the MR head. It is important to ensure that the maximum power dissipation capability of the MR head is not exceeded. Because the MR element operates as a highly sensitive resistance, the power dissipated by the MR element will be proportional to the resistance of the MR element multiplied by the square of the bias current. Accordingly, there is an upper limit on the magnitude of the bias current that can be applied to any given MR head, and the application of too large a bias current, even momentarily, can stress the MR head and adversely affect its operational reliability over time.
Thus, in order to optimize the performance of the MR head, the maximum bias current that can be safely applied to the MR head must be determined. The accuracy in determining this optimal bias current depends directly on the accuracy in measuring the resistance of the MR head; the greater the accuracy of the MR head resistance measurement, the greater the accuracy that can be achieved in determining the optimal bias current. In this way, accurate measurement of the MR head resistance is crucial for optimal MR head performance.
Accordingly, there is a need for a magnetic data storage and retrieval system that measures the resistance of the MR head with greater accuracy in order to optimize the bias current to the MR head.
The present invention is a magnetic data storage and retrieval system. A preamplifier circuit is operably coupled to a magnetoresistive head and a resistor, and applies a first current to the magnetoresistive head and a second current to the resistor. A voltage measurement circuit measures a first voltage across the magnetoresistive head and a second voltage across the resistor. A resistance calculation circuit calculates a resistance of the magnetoresistive head based upon the first and second voltages.